Three times over the last 2.1 million years, the terrifying supervolcano beneath Yellowstone National Park has erupted with force a thousand times more powerful than Mount St. Helens. That deadly zit on America's face just "sighed." Stay asleep, volcano!

You read that right: the whole of Yellowstone National Park was formed the last time the supervolcano erupted over 640,000 years ago. The park itself is actually the caldera of one of the largest volcanoes on earth, and thus if that sucker erupts, we are in danger, girl.

Fans of Bill Bryson may recall the author's gleeful recounting of the myriad ways that the earth could blow up and we all could be destroyed in his readable, entertaining A Short History Of Nearly Everything. Nerds of geology may note that there's no way for us to glean when, exactly the Yellowstone supervolcano might erupt; we don't have the instruments, experience, or expertise necessary to predict an eruption on that scale. What we do know is what we can measure, and beginning in 2004, the ground in the park has been rising at the rate of a few inches per year. The rate at which it's rising has slowed in recent years, but the bulge is still cause for mild alarm among some scientists.